1. Field of the Invention
This invention relates to a color separation/synthesis apparatus and a projector apparatus, and more particularly, is suitably applied to a projector apparatus using a plurality of reflective type spatial modulators.
2. Description of the Related Art
In a projector apparatus capable of projecting an image of large screen, emitted light from a bright light source, such as a xenon or metal halide lamp, is introduced into a spatial modulator to be spatially-modulated in accordance with a video signal, and then thus obtained light is enlarged and projected by means of a projection optical system.
In this case, methods for representing a natural image (color image) considered on such a projector apparatus include a first method in which color information is assigned to each pixel (that is, pixels of three primary colors are prepared for each pixel of the video signal) and a second method in which color information is assigned to a display image in the time division scheme (that is, a red component, a green component, and a blue component of a color image are successively displayed with a triple frequency of a frame frequency.
However, the aforementioned first method has a problem in which the resolution is deteriorated by respectively preparing the three pixels for pixels of the video signal, whereas the second method has another problem in which deterioration of images occurs due to the separation of colors accompanying the motion of a glance.
As one approach to solve such problems, there is a way in which white light emitted from a light source is separated into three primary colors to be spatially modulated in accordance with the respective color components of an image by individual spatial modulators.
FIG. 1 shows a general structure of a projector apparatus 1 using transmission type spatial modulators, out of such apparatuses.
Actually, in the projector apparatus 1, white light L1 emitted from a light source 2 is separated into a blue ray L2A, a green ray L2B, and a red ray L2C in a color separation section 3 to be spatially modulated in accordance with the respective color components of an image in corresponding spatial modulators 4A to 4C, and thus obtained blue component L3A, green component L3B and red component L3C of the color image light are synthesized in a color synthesis section 5 and thereafter the resultant color image light L4 is projected via a projection lens 6 to outside.
On the other hand, FIGS. 2 and 3 show a general configuration of a projector apparatus 10 using reflective type spatial modulators, out of the aforementioned projector apparatuses.
Actually, in the projector apparatus 10 shown in FIG. 2, white light L10 emitted from a light source 11 is introduced via a beam splitter 12 into a color separation section 13 to be separated into three primary colors, and the obtained blue ray L11A, green ray L11B, and red ray L11C are spatially modulated respectively in corresponding spatial modulators 14A to 14C. Then, color image light L13 is formed by synthesizing the blue component L12A, green component L12B, and red component L12C of the color image light emitted respectively from the spatial modulators 14A to 14C in a color separation synthesis section 13 and is projected to outside via a beam splitter 12 and a projection lens 15 in order.
Further, in a projector apparatus 20 shown in FIG. 3 in which the same reference numerals are applied to parts corresponding to FIG. 2, the white light L10 emitted from the light source 11 is separated into the blue ray L11A, the green ray L11B and the red ray L11C in a color separation section 21, which are then introduced via the respective beam splitters 22A to 22C into the corresponding spatial modulators 14A to 14C to be spatially modulated. Then, the color image light L13 is formed by synthesizing the obtained blue component L12A, green component L12B, and red component L12C of the color image light in a color synthesis section 23 and is projected to outside via the projection lens 15.
In this way, in the projector apparatuses 10 and 20 using reflective type spatial modulators 14A to 14C, though separation means for separating incident/reflective light of the beam splitters 12 and 22A to 22C becomes necessary, the same face side of the spatial modulators 14A to 14C can be used for the separation and synthesis of colors, so that the apparatus has advantage in that the whole apparatus can be downsized as compared with the apparatus using the transmission type spatial modulators 4A to 4C (FIG. 1).
Meanwhile, in such projector apparatuses 1, 10 and 20 (FIGS. 1 to 3) for respectively separating the white light L1 and L10 from light sources 2 and 11 into three primary colors as mentioned above, a two-color dielectric multilayer film (hereinafter, referred to simply as dielectric multilayer film) is ordinarily employed as color separation and synthesis means for incident light.
FIG. 4 shows the configuration of a projector apparatus 30 using glass as a holding means for the dielectric multilayer film and a reflective type spatial modulation element.
Actually, in the projector apparatus 30, white light L20 from a light source 31 is introduced into a color separation/synthesis section 33 via a beam splitter 32 and is sequentially color-separated by first and second dielectric mirrors 36A and 36B composed by respectively forming dielectric multilayer films 35A and 35B on one side of glass plates 34A and 34B.
Besides, in the projector apparatus 30, blue ray L21A, a green ray L21B and red ray L21C obtained by the color separation are respectively introduced into corresponding first to third spatial modulators 37A to 37C to be spatially modulated in accordance with a video signal which is supplied.
In such manner, in the projector apparatus 30, a blue component L22A, a green component L22B, and a red component L22C of color image light based on the video signal, which are emitted from the first to third spatial modulators 37A to 37C are synthesized by the first and second mirrors 36A and 36B in the color separation/synthesis section 33 and the obtained color image light L23 is emitted to outside via a projection lens 38.
However, such the projector apparatus 30 has problems that astigmatism occurs in component rays (red and green rays) of the white light L20 transmitted through the first and second dielectric mirror 36A and 36B due to the width of the first or second dielectric mirror 36A or 36B, and on the other hand, aberration occurs in component rays (blue and green rays) of the white light L20 reflected from the first or second dielectric mirror 36A or 36B due to stress-strain. In this case, a tradeoff relation between the stigmatism due to the width of the first or second dielectric mirrors 36A and 36B and the aberration due to stress-strain has a problem in that it is difficult to obtain highly resolution images as projected images.
As one approach to solve such problems, as shown in FIG. 5 in which the same reference numerals are applied to parts corresponding to FIG. 4, there is a way to use glass blocks 42A to 42C as a holing means for dielectric multilayer films 41A and 41B. The way has advantage in which the stress can be reduced as compared with a case of using a glass plate as a holding means for dielectric multilayer film and also has advantage in which the length of an optical path to the projection lends 38 can be shortened. Note that, FIGS. 6 and 7, in which the same reference numerals are applied to parts corresponding to FIG. 5, show the configuration of a projector apparatus using spatial modulators in which it is necessary to unify the number of reflections (all to odd or even) during the synthesis of colors.
However, projector apparatuses 40, 50, and 60 using glass blocks 42A to 42C or 60A to 60D as a holding means for such dielectric multilayer films 41A and 41B have problems in that the large glass blocks 42A to 42C and 60A to 60D are heavy and expensive, and also have an essential problem in that the color purity of separated and formed blue ray L21A, green ray L21B, and red ray L21C is insufficient.
This reason is that the wavelength characteristic of a dielectric multilayer film generally has a certain degree of rising width "W" as shown in FIG. 8, and in the case where the white light is irradiated to the dielectric multilayer film with an incidence angle of 45.degree., the component rays of the wavelength range of intermediate colors included in the white light L20 are mixed with the transmitted light and reflected light of the dielectric multilayer films 41A to 41C (FIGS. 5 to 7) because the rising width "W" for the white light L20 incident to the dielectric multilayer films 41A to 41C having both sides in contact with glass blocks 42A to 42C or 60A to 60D (FIGS. 5 to 7) is wider than that of the dielectric multilayer films 35A and 35B formed on one side of the glass plates 34A and 34B (FIG. 4) (in the latter, another side of the dielectric multilayer films 35A and 35B faces the air having a refractive index of one).
Furthermore, for example, the projector apparatuses 50 and 60 using spatial modulators 51A to 51C with the need for unifying the number of reflections of individual colors during the color synthesis as shown in FIGS. 6 and 7, have problems of difficulty in the downsizing of the whole apparatus and the simplification of a configuration because an additional mirror 52 (FIG. 6) is required or large-sized glass blocks 60A to 60D of the color separation/synthesis section 61 (FIG. 7) are required as compared with the projector apparatus 40 (FIG. 5) using spatial modulators 37A to 37C (FIG. 5) without need for unifying the number of reflections.
As an improvement method for such a poor color purity, by utilizing the smaller the incidence angle to the dielectric multilayer films 41A and 41B, the narrower is the raising width "W" (FIG. 7) for the incident light of the dielectric multilayer films 41A and 41B, the incidence angle .theta..sub.1 of the incident light for the dielectric multilayer films 72A and 72B seems to be smaller than 45.degree. as shown in FIG. 9 in which the same reference numerals are applied to parts corresponding to FIG. 5.
However, there is a problem that the volume of a glass block abruptly becomes larger than the size of a spatial modulator generally if the incidence angle of white light to a dielectric multilayer film deviates from 45.degree. and accordingly there occurs a problem of difficulty in the downsizing and weight reduction of a projector apparatus. Actually, for example, in FIG. 9, with reducing the incidence angle .theta..sub.1 of white light L20 to the dielectric multilayer films 72A and 72B, the second spatial modulator 37B comes into touch with the adjacent glass block 71A and accordingly the glass block 71B must be made large in size to avoid this.
Especially in the case where the spatial modulators 51A to 51C (FIGS. 6 and 7) with the need for unifying the number of reflections to even or odd times during the synthesis is used to construct a projector apparatus, a large glass block is required or an additional mirror is necessary in comparison with a case of using the spatial modulators 37A and 37B (FIG. 9) without need for unifying the number of reflections as described above, and accordingly this presents a serious problem in considering the downsizing of the whole projector apparatus.
As method for solving such problems, for example, by utilizing color separation means employed in three plate type CCD camera, as shown in FIG. 10 in which the same reference numerals are applied to parts corresponding to FIG. 5, it is considered that two triangularprism glass blocks 81A and 81B and a quadrilateral prism glass block 81C of trapezoid bottom are used to construct a color separation/synthesis section 80 in such a manner that the blue ray L21A and green ray L21B obtained by the color separation of white light L20 are (totally) reflected from other places than the dielectric multilayer films 82A and 82B in the corresponding glass blocks 81A and 81B.
The method has advantage in that the color purity of projected images can be improved and moreover the size of the glass blocks 81A to 81C can be small in comparison with a simple usage described in FIG. 9 because the incidence angle .theta..sub.2 to the respective dielectric multilayer films 82A and 82B can be set to about 30.degree. This reason is that, as can be seen from FIGS. 11A and 11B, the volume of a glass block can be reduced to half by the reflection of a transmitted ray even for the same length of an optical path.
However, this method has the following problems.
Let the wavelength characteristic of the second dielectric multilayer film 82B is such as shown in FIG. 8. When light having the wavelength .lambda..sub.C is separated by the second dielectric multilayer film 82B, 50% of the light is reflected from the second dielectric multilayer film 82B and enters the second spatial modulator 37B and the rest 50% is transmitted through the second dielectric multilayer film 82B and enters the third spatial modulator 37C. Then, the two pieces of light are respectively reflected from the corresponding second or third spatial modulator 37B or 37C.
In this case, out of the ray L22B returned to the second dielectric multilayer film 82B from the second spatial modulator 37B, 50% travels toward a projection lens (not shown) by being reflected from the second dielectric multilayer film 82B, but the rest 50% (25% of the original light), ray L30A, is transmitted through the second dielectric multilayer film 82B and enters the third spatial modulator 37C. And similarly, out of the ray L22C returned to the second dielectric multilayer film 82B from the third spatial modulator 37C, 50% is transmitted through the second dielectric multilayer film 82B and travels toward the projection lens, but the rest 50% (25% of the original light), ray L30B, is reflected from the second dielectric multilayer film 82B and enters the third spatial modulator 37C.
If rays L30A and L30B different in the state of transmitting and reflection at the separation and synthesis (hereinafter, referred to as unnecessary rays) enter other spatial modulators 37A to 37C like this, the deterioration of projected images in contrast occurs due to scatter or the like and the color purity of projected images is also affected.
In addition, in the projector apparatus having a color separation/synthesis composed as described above, as can be seen from FIG. 10, a gap 83 is provided between the glass block 81B and the glass block 81A in order to totally reflect green ray L22B reflected from the second dielectric multilayer film 82B inside the glass clock 81B, but if the gap 83 is not adequately small, there are problems that astigmatism occurs and the slenderness ratio of a projected image changes.
Note that, though the influence is small, unnecessary rays may occur in the separation of white light at the first dielectric multilayer film 82A or in the synthesis of the respective rays L22A to L22C from the first to third spatial modulators 37A to 37C.
Thus, in a projector apparatus using a color separation/synthesis section 80 as shown in FIG. 10, since a part of light within the rising range of wavelength for the first and second dielectric multilayer films 82A and 82B become unnecessary rays, it is desirable to use a first and second dielectric multilayer film having a rising range as narrow as possible, but the rising range cannot be made "0" in practice.